unmountable boot error

Ok, I have a dimension 2400 and since I brought the PC almost two years ago I have had numerous problems with it - generally the same problem each and every time.

Basically the PC will be running fine and then all of a sudden upon starting up the PC I get a black screen saying something about my computer not being able to start normally, and it gives me 5 options

- start in safe mode

- start in safe mode with networking

- start in safe mode wih command prompt

- last known good configuration

- start windows normally

None of these options work.  If I choose the 'last known good configuration' or 'start windows normally', the Windows screen appears, then it goes to a blue screen giving a few error codes and says 'UNMOUNTABLE_BOOT_ERROR'

If I choose to enter in 'safe mode'/'safe mode with command prompt' it shows a list of file names and stops and goes no further.

I have also tried running a driver diagnostic, and had a few errors come up:

ERROR CODE 0F00 : 1344 : BLOCK 100480 : UNCORRECTABLE DATA ERROR OR MEDIA IS WRITE PROTECTED.

and then another error code with the same uncorrectable data....etc and then it stops at about 77% and goes no further.

This is the 7th or 8th time we've had a problem similar to this although safe mode not working and the diagnostic error messages are new problems.

Each and every time we've lost everything on the PC - re installed only for it to mess up 1,2,3,4 months down the line!